In a plasma processing apparatus of the inductively coupled plasma (ICP) type, a construction that an upper portion of the chamber is closed with a dielectric plate, and a coil to which a radio frequency power is applied is placed on the dielectric plate is known. For example, Patent Literatures 1 to 3 disclose plasma processing apparatuses in which the dielectric plate is reduced in thickness while the mechanical strength is secured by supporting the lower surface side of the dielectric plate with a beam-shaped structure. Also, Patent Literatures 4 and 5 disclose constructions for supplying gas from a dielectric-plate supporting structure.
In these plasma processing apparatuses, since the dielectric plate is thin and the beam-shaped structure is so shaped as to reduce interaction with the coil, a high-density plasma can be generated.
In recent years, in order to subject a Si substrate to deep Si etching, i.e. deep dipping, high-aspect etching or the like at high speed, it is desired to further increase the plasma density, for example, by increasing the internal pressure of the plasma processing apparatus to, for example, about 10 Pa or higher and moreover increasing the applied radio frequency power.
However, such high-pressure, high-power Si etching process as shown above would involve very considerable etching or wear of the dielectric plate made of quartz. In conventionally proposed plasma processing apparatuses including those disclosed in Patent Literatures 1 to 5, not enough considerations are given to effective suppression of etching or wear of the dielectric plate based on the process characteristics of such high-pressure, high-power, process.
Generally, the gas flow state can be classified into a molecular flow region under low pressure (high degree of vacuum), a viscous flow region under high pressure (low degree of vacuum), and an intermediate flow region being an intermediate region between the molecular flow region and the viscous flow region. In a plasma processing (hereinafter, referred to as “high-pressure process”) under such a high pressure that the gas flow falls within a range from the intermediate flow region of the molecular flow region and the viscous flow region to the viscous flow region, the gas flow tends to be more viscous so that the position of a gas introducing port and the introduction method affect the etching characteristics to more extent, in comparison to a plasma processing (hereinafter, referred to as “low-pressure process”) under such a high pressure that the gas flow falls within the molecular flow region. In the high-pressure process, for example, a relative positional relationship between a process gas flow and a high plasma density region largely affects the efficiency of plasma generation from the process gas. Also in the high-pressure process, a relative positional relationship between the process gas flow and the substrate largely affects the amount of radicals or ions fed to the substrate as well as their in-plane distribution. However, in conventionally proposed plasma processing apparatuses including those disclosed in Patent Literatures 1 to 5, not enough considerations are given to improvement of the processing rate such as etching rate based on the characteristics of the high-pressure process, as well as to uniformization of processing characteristics such as etching rate distribution.
Patent Literature 1: JP 3384795 B
Patent Literature 2: JP 3729939 B
Patent Literature 3: JP 2001-110577 A
Patent Literature 4: JP 2005-122939 A
Patent Literature 5: JP 2003-332326 A